The vast majority of headaches presenting to emergency or primary care are benign primary disorders (tension-type, migraine, cluster). However, a subset of headaches are secondary to life-threatening pathology — subarachnoid hemorrhage (SAH), meningitis, hypertensive emergency, intracranial mass, venous sinus thrombosis, temporal arteritis — where delayed diagnosis results in permanent disability or death. The nurse's role is to identify "red flag" features that mandate emergent escalation rather than symptomatic treatment. The single highest-stakes red flag in nursing practice: The "thunderclap headache" — sudden-onset worst headache of the patient's life, reaching maximal intensity within 60 seconds — represents SAH until proven otherwise. This patient requires emergent CT head without contrast and lumbar puncture within 12 hours of symptom onset regardless of CT result. Top 3 nursing priorities: 1. Distinguish thunderclap or progressively worsening "new worst headache" from the patient's typical headache pattern — any deviation demands urgent physician/NP notification. 2. Perform a rapid targeted neurological assessment (GCS, cranial nerve exam, meningeal signs — Kernig's, Brudzinski's) and obtain vital signs including temperature before administering any analgesia. 3. Prepare for emergent CT head, IV...